The United States Military, as well as many other Security Forces ranging from police to private security details in addition to NASA are in dire need of high temperature transparent armor, tubing, sheet and rods. Sapphire is an engineered material for high temperature transparent applications. Sapphire has a high melting point close to 2,053° C. and can be used above 2,000° C. Single crystal alpha alumina typically referred to as sapphire can be found in nature. Sapphire is aluminum oxide (α-Al2O3). However, for use in transparent armor or transparent tubing, sheets, piping and/or rods it is typically grown starting with a crystal seed. The formation of single crystal sapphire can be accomplished using techniques such as the Czochralski Method, Edge-Defined Film Fed Growth (EFG), or Kyropoulos Method, or other techniques depending upon the desired size and shape of the boule, and the orientation of the crystal. Hence, the cost of synthetically grown sapphire is very expensive.
A severe disadvantage for using sapphire is that it can only be grown to certain dimensions for tubing, rods and sheets. Consequently, to manufacture larger parts, the small sapphire sheets or windows must be joined together to make a large window. Likewise, tubing can only be grown to certain diameters and lengths. Consequently, two or more tubes must be joined to make a longer tube.
With the ever-increasing use of Improvised Explosive Devices (“IEDs”) there exists an immediate need for transparent armor. However, the lack of a joining and/or welding process for sapphire has hindered its use and thus limited its use for small windows. Heretofore, the word “welding” will be used to encompass a means for joining sapphire by sintering, melting and/or fusing separate sapphire pieces such as whole sheets, tubes, rods or as separate individual granular or bead material such as crushed boule, alumina powder or green alumina ceramic beads by means of coalescence.
Although many other joining processes can be enumerated, in order to be brief the term “welding” and “plasma arc welding” as used herein refers to sintering, fusing and in particular coalescence of materials due to heating.
Plasma is primarily used for cutting metal, plasma spraying, analysis of gases via IC Mass Spectrometry, plasma TVs, plasma lighting and expensive production of nanopowders. One of the major drawbacks for using plasma for other applications is the complexity and cost of existing systems. As a result, current plasma systems are not widely used for steam reforming, cracking, gasification, partial oxidation, pyrolysis, heating, melting, sintering, rich combustion and/or lean combustion.
The major unresolved issue with current commercially available plasma torches that use inertia confinement is that there is only one fluid exit—through the nozzle—for confining the plasma. Moreover, these systems must rely on controlling or regulating the upstream gas flow in order to ignite, sustain and confine the plasma. These problems have plagued the plasma industry and thus plasma torches are viewed as difficult to operate due to the power supplies, controls, gases and valves associated with the torches. The problem associated with valves and gas regulators is evermore pronounced with plasma arc welding (“PAW”). The use of valves and regulators for plasma cutting are much larger and flow more gas then the regulators for plasma arc welding. Likewise, the power supplies associated with plasma arc welding operate at lower voltages then plasma cutting. Keyhole plasma arc welding requires very high power levels. Consequently, plasma arc welding ceramics requires full penetration to an electrically conductive material if the plasma arc welder is operated in a transferred-arc mode.
Accordingly, there is a need for a plasma system that is less complex, lower in cost and more efficient than current systems in order for plasma to be accepted as a mainstream device for use in the aforementioned applications and processes, for example welding ceramics and non-conductive materials, such as sapphire.